1. Field of the Invention
This invention relates to a container crane for performing cargo work.
2. Description of the Prior Art
In performing cargo work for containers loaded in a ship, normally a container crane is used. For example, a container crane 1 show in FIG. 1 of the accompanying drawings includes a trolley 2 mounted for horizontal movement thereon and a spreader 3 suspended on the trolley 2. Thus, containers 5 on a ship 4 can be transferred to a bogie truck 7 on land 6 by the spreader 3.
In other to avoid possible collision of the spreader 3 with any of the containers 5, the spreader 3 is transported along a safe route A as shown in FIG. 1. In particular, in order to transport the containers 5 in several rows, the spreader 3 must be moved along the roundabout route A. Accordingly, a problem exists in that the working efficiency of the spreader 3 is low.
There is a current trend of automating container cranes. For such automation, positions of containers on a ship must be identified with accuracy. However, since a ship is normally rolling from various causes such as current, it is difficult to identify positions of containers on a ship relative to a position on the ground.